Abstract
Somatic embryogenesis is being piloted for the commercial production of genetically improved Norway spruce (Picea abies L. Karst) forest regeneration material in Finland. The main challenge to making the process commercially relevant is the dependence on time-consuming and highly skilled manual labor. Automation and scaling up are needed to improve cost-effectiveness. Moving from the proliferation of embryogenic tissue on semisolid media to suspension cultures could improve process scalability. In a series of four experiments (overall, with 20 cell lines, 4–9 per experiment), the suitability of proliferation in suspension culture for Norway spruce somatic embryogenesis was evaluated based on the growth rate, indicators of stress conditions, good-quality cotyledonary embryo yield, and embling survival in a greenhouse. The proliferation rate in suspension was found equal to on semisolid media, but with a remarkable genotypic variation. Embryogenic tissue matured directly without pre-treatments from suspension onto semisolid media produced lower numbers of good-quality embryos than tissue matured from semisolid media. Rinsing the suspension-grown tissue with hormone-free liquid media before maturation improved embryo yield, bringing it closer to that of semisolid-grown tissue. Decreasing 6-benzylaminopurine and 2,4-dichlorophenoxyacetic acid concentrations in suspension proliferation media to 0.5 or 0.1 times those in semisolid media did not affect tissue growth and did not improve embryo production. The hydrogen peroxide (H2O2) content and guaiacol peroxidase activity were elevated in suspension cultures compared with semisolid medium, which had the same plant growth regulator content. In one experiment out of four, the greenhouse survival of germinants was lower when proliferation was carried out in full strength suspension than on semisolid media; in other experiments the survival rates were equal.
Highlights
The demand for tree biomass and timber has increased due to the growing need for substitutes for fossil fuels (FAO, 2008; Lauri et al, 2014), for example
The Plant growth regulators (PGR) concentrations were reduced in the subsequent Experiments II, III, and IV in an attempt to improve maturation results
The growth of embryogenic tissue (ET) was decreased by Forced aeration (FA), but this can be at least partly attributed to agitation from aeration throwing tissue out of the medium onto the culture bottle walls, and the difference was not statistically significant
Summary
The demand for tree biomass and timber has increased due to the growing need for substitutes for fossil fuels (FAO, 2008; Lauri et al, 2014), for example. To most efficiently implement the results achieved by tree breeding, materials derived via vegetative, i.e., asexual, propagation could be used to enable the production of plants of uniform quality and known selected characteristics (Bonga, 2016). Somatic embryogenesis has become the method of choice for the vegetative propagation of conifers due to its high multiplication rate and the maintenance of the juvenility of cell lines via cryopreservation (Park, 2002). Automation and increased production volume are needed to make somatic embryogenesis (SE) a commercially profitable way to produce forest regeneration material (Gupta and Timmis, 2005; Denchev and Grossnickle, 2019; Egertsdotter et al, 2019)
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